Characterization and Modification of a Novel, Highly Soluble Flavonoid 3′-OH Glycosyltransferase from Lactuca sativa and Its Application in the Efficient Biosynthesis of flavonoid-3′-O-glucoside

Luteolin-3'-O-glucoside, a rare glycosylated form of luteolin, exhibits diverse biological activities. However, its natural abundance in plants is extremely low, which hampers its application potential in the food and medical fields. Biological transformation is an effective way, but the scarcity of glycosyltransferases capable of catalyzing flavonoid 3'-OH poses a challenge to the biotransformation of this functional group. In this study, Ls3'GT from Lactuca sativa was successfully cloned and expressed, which efficiently converted luteolin to luteolin-3'-O-glucoside. Ls3'GT exhibited high solubility and broad substrate specificity. A mutant Ls3'GT-E347V with regioselectivity from 3'-OH to 7-OH and a mutant Ls3'GT-R461A with increased k_cat/K_m by 84% were obtained by site-directed mutagenesis. Through the analysis of the structure and bioinformatics of Ls3'GT, the expression of the enzyme was affected to different degrees by truncating loop1, loop2, and loopN, respectively. Under optimal conditions and utilizing the synthetic pathway of UDPG, the recombinant strain successfully converted 3.25 g/L luteolin to 4.72 g/L luteolin-3'-O-glucoside, with a remarkable space-time yield of 65.6 mg/L/h, which marked the highest reported yield for the biosynthesis of luteolin-3'-O-glucoside to date. This study offers an efficient and straightforward approach for the biosynthesis of flavonoid-3'-O-glucoside, which holds great promise for food and pharmaceutical applications.